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1066 Chapter 19 | Transition Metals and Coordination Chemistry
The common compounds that we have just discussed can also be used to prepare salts. The reactions involved include
the reactions of oxides, hydroxides, or carbonates with acids. For example:
Substitution reactions involving soluble salts may be used to prepare insoluble salts. For example:
In our discussion of oxides in this section, we have seen that reactions of the covalent oxides of the transition elements
with hydroxides form salts that contain oxyanions of the transition elements.
How Sciences Interconnect
High Temperature Superconductors
A superconductor is a substance that conducts electricity with no resistance. This lack of resistance means that there is no energy loss during the transmission of electricity. This would lead to a significant reduction in the cost of electricity.
Most currently used, commercial superconducting materials, such as NbTi and Nb3Sn, do not become superconducting until they are cooled below 23 K (−250 °C). This requires the use of liquid helium, which has a boiling temperature of 4 K and is expensive and difficult to handle. The cost of liquid helium has deterred the widespread application of superconductors.
One of the most exciting scientific discoveries of the 1980s was the characterization of compounds that exhibit superconductivity at temperatures above 90 K. (Compared to liquid helium, 90 K is a high temperature.) Typical among the high-temperature superconducting materials are oxides containing yttrium (or one of several rare earth elements), barium, and copper in a 1:2:3 ratio. The formula of the ionic yttrium compound is YBa2Cu3O7.
The new materials become superconducting at temperatures close to 90 K (Figure 19.10), temperatures that can be reached by cooling with liquid nitrogen (boiling temperature of 77 K). Not only are liquid nitrogen-cooled materials easier to handle, but the cooling costs are also about 1000 times lower than for liquid helium.
Figure 19.10 The resistance of the high-temperature superconductor YBa2Cu3O7 varies with temperature. Note how the resistance falls to zero below 92 K, when the substance becomes superconducting.
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